1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a digital rights management (DRM), and more particularly, to playing back content based on DRM between a portable storage and a device, and the portable storage for the same.
2. Description of the Related Art
Recently, DRM has been actively researched and developed. Commercial services using DRM have already been used or will be used. DRM needs to be used because of the following various characteristics of digital content. That is to say, unlike analog data, digital content can be copied without loss and can be easily reused, processed, and distributed, and only a small amount of cost is needed to copy and distribute the digital content. However, a large amount of cost, labor, and time are needed to produce the digital content. Thus, when the digital content is copied and distributed without permission, a producer of the digital content may lose profit, and the producer's enthusiasm for creation may be discouraged. As a result, development of digital content business may be hampered.
There have been several efforts to protect digital content. Conventionally, digital content protection has been concentrated on preventing non-permitted access to digital content, permitting only people paid charges to access the digital content. Thus, people who paid charges for the digital content are allowed to access unencrypted digital content while people who did not pay charges are not allowed to access the unencrypted digital content. However, when a person who paid charges intentionally distributes the digital content to other people who did not pay charges, the digital content can be used by the other people who did not pay charges. To solve this program, DRM was introduced. In DRM, anyone is allowed to freely access encoded digital content, but a license referred to as a rights object (RO) is needed to decode and execute the digital content. Accordingly, the digital content can be more effectively protected by using DRM.
The concept of DRM will be described with reference to FIG. 1. DRM relates to management of contents (hereafter, referred to as encrypted contents) protected using a method such as encryption or scrambling and ROs allowing access to the encrypted contents.
Referring to FIG. 1, a DRM system includes user devices 110 and 150 wanting to access content protected by DRM, a contents issuer 120 issuing content, a rights issuer 130 issuing an RO containing a right to access the content, and a certification authority 140 issuing a certificate.
In operation, the user device 110 can obtain desired content from the contents issuer 120 in an encrypted format protected by DRM. The user device 110 can obtain a license to play back the encrypted content from an RO received from the rights issuer 130. Then, the user device 110 can play back the encrypted content. Since encrypted contents can be circulated or distributed freely, the user device 110 can freely transmit the encrypted content to the user device 150. The user device 150 needs the RO to play back the encrypted content. The RO can be obtained from the rights issuer 130. Meanwhile, the certification authority 140 issues a certificate indicating that the contents issuer 120 is authentic and the user devices 110 and 150 are authorized devices. The certificate may be embedded into devices used by the user devices 110 and 150 when the devices are manufactured and may be reissued by the certification authority 140 after a predetermined duration has expired.
DRM protects the profits of those producing or providing digital contents and thus may be helpful in activating the digital content industry. However, there is inconvenience practically in this DRM system although an RO or encrypted content can be transferred between the user devices 110 and 150 using mobile devices. In this situation, ROs and encrypted contents can be easily moved between devices when a portable storage is used. In other words, a method that enables a device to use an RO stored in a portable storage to access content protected through DRM is desired.